Controlling the electronic properties of polythiophene through the insertion of nonaromatic thienyl S,S-dioxide units

A new class of thiophene-based polymers characterized by the presence of one nonaromatic thienyl S,S-dioxide moiety (O) to every two, four, and six aromatic thienyl units (T) was prepared from the newly synthesized precursors TOT, TTOTT, and TTTOTTT, and electrochemically characterized. The polymers displayed remarkably greater electron affinities than that of polythiophene and could be reversibly n-doped at moderate potentials, while still maintaining the property of also being p-doped at moderate potential values. All polymers were characterized by good p-doping/undoping cyclability, while at least four aromatic units to every nonaromatic one were needed to ensure good n-doping/undoping cyclability. ZINDO/S//PM3 calculations on TOT, TTOTT, and TTTOTTT and on (TOT)(3) and (TTOTT)3, as models for the corresponding polymers, showed that the presence of the nonaromatic units does not affect the pi,pi* character of the frontier orbitals but decreases their energy, in particular that of the LUMO. The calculations allow the cyclability properties of the polymers in the p- and n-doping domains to be rationalized in terms of delocalization of the electronic charge of p- and n-type charge carriers over the aromatic units.